Attached Above Garage ADU Guide

Key Takeaways

• Above-garage ADUs, also known as second-story ADUs or accessory dwelling units above garages, have become an attractive option for homeowners looking to add extra space for a home office, generate rental income, or create a separate living unit for adult children.
• While converting an existing detached garage into a 1-story ADU is more cost-effective, homeowners often appreciate how the above-garage design allows them to maintain parking and preserve yard space.
• These types of ADUs aren’t without their building challenges, though. For starters, they aren’t always allowed by homeowner’s associations or even local building departments, and if they are, construction typically involves the work of a structural engineer, which can add time and cost to the overall project.

High-end finishes not only personalize your ADU but also boost its rental appeal and long-term property value.

What is a Garage ADU?

A garage ADU, or a garage accessory dwelling unit, refers to a secondary housing unit that utilizes the existing garage space, either through a complete conversion or by building above it.

Homeowners on a tight budget and/or looking to use this additional dwelling unit as a granny flat may choose to convert their entire garage into an ADU to save money on materials and create an accessible, 1-story cottage. Homeowners can convert their detached or attached garage. An attached garage conversion that is under 500 square feet is known as a garage JADU, or junior accessory unit. You can read more about the difference here.

Homeowners with a larger budget who want to still use their garage for parking or storage and are dealing with limited space on the lot may opt to build their ADU above the garage. These above-garage ADUs are popular as rental units, apartments for adult children, and home offices.

Garage ADUs are a smart way to repurpose existing space—ideal for homeowners wanting a budget-conscious and space-efficient upgrade.

Advantages of Building an Above-Garage ADU

Building an above-garage ADU transforms underutilized vertical space into additional living space, offering many advantages to homeowners, including:

• Preserving yard space. Especially in urban areas like San Diego, yard space is at a premium. Taking advantage of vertical space gives you extra living space without adding to your footprint.
• Rental potential. These types of units can be attractive to potential renters, allowing for tens of thousands of dollars in passive income every year.
• Quiet retreat for work and guests. These second-story units can often be quieter than those on the ground level, with additional separation from the main residence, making them a quiet escape for a home office or guest suite.
• Increased property value. Whatever the ultimate use for the space (rental unit, space for family members, home office), you’re ultimately adding more livable square footage to your property, which offers a great overall return on investment.

Building up lets you preserve your lot’s footprint while increasing livable space—perfect for tight urban settings like San Diego.

Things to Consider Before Building an ADU Over Your Garage

Given the uniqueness of these builds, there are many things to consider before breaking ground on construction, things like:

• Local building codes. While municipalities have made building ADUs easier to combat the state’s housing crisis, many place limitations when it comes to 2-story ADUs. Some ban 2-story builds outright, and some only allow them if your existing home is also 2 stories.
• Homeowner’s association bylaws. While HOAs can’t ban ADUs entirely, they can place limitations on height, which can restrict your ability to build above your garage.
• Structural integrity. Before you build on top of your garage, you’ll need to assess its integrity to make sure it can support the additional weight. If it can’t, additional measures must be taken before you begin building. This is something that’s best accessed by a structural engineer.
• Intended use. If you’re hoping to use your ADU to house elderly family members, a second-story unit might not be the best option for long-term accessibility. When it comes to mother-in-law suites, most homeowners opt for a single-story ADU design.

Structural readiness is key—expect to reinforce or upgrade your existing garage foundation before building upward.

Cost and Investment for Building an ADU Above a Garage

While construction costs for a full garage conversion range between $150,000 and $250,000, building a new unit above your existing garage is more costly, ranging anywhere between $250,000 – $400,000.

Where your build falls in this range depends on things like:

• The structural integrity of your existing garage and what repairs or supports may need to be made or added
• The square footage of your unit, with larger units resulting in a larger cost
• The number of bathrooms (typically 1 vs 2, with 2 resulting in additional cost)
• The design finishes

While most homeowners find the cost worthwhile, given the increase in property resale value and rental potential, it’s still a significant amount to invest upfront. Most homeowners don’t have the construction costs available as cash. Luckily there are many financing options available to homeowners, from an equity loan to a construction loan. You can read more about potential financing options here.

Elegant finishes like bold cabinetry and lighting elevate your ADU’s value—investing in design details pays off in both ROI and lifestyle.

Common Uses for Above-Garage ADU

Above-garage ADUs are incredibly flexible living spaces. Homeowners we’ve worked with have used their above-garage builds as:

• Long-term rentals
• Apartments for adult children
• Guest houses
• Home office
• Workout spaces
• Art studios/hobby spaces

The Construction Process: Building an ADU Above Your Garage

Most detached, 1-story ADUs can be built within 8-12 months, from initial planning to final move-in. Above-garage ADUs fall into the upper end of this range for a few reasons.

Firstly, planning and permitting for these types of ADUs is more complex, taking 3-4 months. This includes the initial consultation with a structural engineer and any revisions to the plans as dictated by the local building department.

Construction can also take a few weeks longer than more traditional ADU builds, as it often begins by shoring up the existing garage to meet the structural requirements necessary for building on top of it.

Expect longer timelines than ground-level units due to engineering, permitting, and foundational upgrades unique to over-garage ADUs.

Effective Planning and Design for an ADU Above Your Garage

A well-designed above-garage ADU follows the design best practices for any ADU. These include:

• Maximizing light through bright colors and windows
• U-shaped or L-shaped kitchens to maximize cabinet space
• Open-concept kitchen-living rooms
• Adding built-ins and other smart storage solutions

However, these types of ADUs have unique design considerations, too. For example, many homeowners opt to build a smaller ADU, allowing them to incorporate a roof deck into the design. You also have to consider how people will access the second floor and what that will ultimately look like.

Small ADUs benefit from bold, intentional design—maximize function without sacrificing elegance or usability.

Alternative ADU Options

If a vertical build isn’t right for you, either due to cost or limitations with local code, you still have options to preserve green space while creating more living space. The two most popular alternatives to above-garage ADUs are:

• Full garage conversions
• Junior ADUs, where a basement, attached garage, or extra bedroom space is converted to an independent living space

Better Place Design & Build for Expert Garage-Top ADUs

At Better Place Design & Build, we can help you bring an unused garage to life, with an above-garage ADU tailored to your specific needs.

Whether you’re starting your ADU project to gain extra living space for family, rental housing, or a home office, our team offers custom designs, transparent pricing, and unmatched expertise across Southern California and San Diego. Every successful project starts with a free consultation. Schedule yours today to see how we can bring your vision to life.

Working with a turnkey ADU team streamlines planning, ensures compliance, and delivers a cohesive final product from day one.